The present invention lies in the field of steam turbines. More particularly, it relates to a combined gas and steam turbine power plant. In addition, the present invention relates to a method of feeding bypass steam into the steam turbine.
In power plant technology, power plant types may be differentiated according to their type of power generation or according to their field of application. One power plant type includes the industrial power plant, which generates current only as a secondary product. However, the more important energy product is the heating energy or the process steam for industrial or chemical processes.
Examples of a power plant type for commercial power generation include the steam-turbine power plant or the gas-turbine power plant.
A combination of a steam-turbine process with a gas-turbine process leads to a xe2x80x9ccombined-cycle processxe2x80x9d, in which at least one gas turbine is interconnected with a steam turbine. The power-generation efficiencies, which can be achieved thereby are comparatively high. Such a combined gas and steam turbine power plant is also termed a combined-cycle power plant.
However, a disadvantage of the combined-cycle power plants is that the quantity of electricity, which can be generated, depends to a great extent on the gas turbines. Gas turbines are standardized products, whose output or power generation depends significantly on ambient conditions, such as ambient temperatures. Even including the downstream steam-turbine process, the quantity of electricity generated, for example in the summer, is only about 80% of the quantity of electricity generated in the winter.
However, it is sometimes necessary for a higher quantity of electricity to be generated even in the summer months, than which can be delivered by the combined-cycle process: for example, in the event of an increased demand for electricity, during this period due to air-conditioning units being connected to the system. In order to meet this extra demand for electricity, combined-cycle power plants having supplementary firing are used. A steam generator, also called a heat recovery boiler in combined-cycle power plants, is not only fed with hot exhaust gases from the gas turbine, but is also loaded with an additional energy input by the combustion of a fossil fuel. Accordingly, the heat recovery boiler can produce a correspondingly larger steam quantity as xe2x80x9clive steamxe2x80x9d and also achieve a higher live-steam pressure. The output of the steam turbine increases accordingly, but the heat recovery boiler, the live-steam lines and other components of the live-steam path must be designed in accordance with this comparatively rare, but maximum, live-steam state.
The design is therefore affected by unusual conditions. The xe2x80x9c100% load casexe2x80x9d, at comparatively low values of the live-steam pressure, leads to a decreased efficiency of the combined-cycle power plant. In addition, the combined-cycle power plant is equipped with components of comparatively large dimensions, which are more expensive.
It is accordingly an object of the present invention to provide a steam turbine and a method of feeding bypass steam that overcome the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and that has an increased output with a comparatively low technical outlay.
With the foregoing and other objects in view, there is provided, in accordance with the present invention, a steam turbine including at least one valve arrangement, the valve arrangement having at least one quick-closing valve and at least one live-steam control valve, the live-steam control valve being assigned to the quick-closing valve is provided. A steam-turbine inlet region, a high-pressure region, and a first turbine moving-blade row, a live-steam bypass having at least one bypass line and a bypass feed are provided. The bypass feed is coupled to the bypass line. The live-steam bypass feed live steam as bypass steam into the high-pressure region, after the first turbine moving-blade row, as viewed from downstream of the steam-turbine inlet region. At least one bypass control valve is also provided. Further, both the at least one live-steam control valve and the at least one bypass control valve are assigned to the at least one quick-closing valve.
In accordance with another feature of the present invention, the at least one bypass control valve, the at least one quick-closing valve and the at least one live-steam control valve are disposed in a common valve casing.
In accordance with another feature of the present invention, the live-steam bypass includes precisely one bypass line and precisely one bypass feed.
In accordance with another feature of the present invention, the top steam turbine further includes a top steam-turbine outer casing.
In accordance with another feature of the present invention, the at least one bypass feed is disposed in the high-pressure region such that a dismantling of the bypass feed is avoided during a dismantling of the top steam-turbine outer casing.
In accordance with another feature of the present invention, there is provided at least two adjacent blade rows and a bypass inlet region. The bypass feed feeds bypass steam into the high-pressure region through the bypass inlet region. The bypass inlet region is freely selectable in an axial direction between the two adjacent blade rows.
In accordance with another feature of the present invention, there is provided a torus-like annular space, a U-shaped profile element, an inner casing, a turbine shaft section, and a blade passage disposed between the inner casing and the turbine shaft section. The torus-like annular space is defined by an outside diameter and an inside diameter.
In accordance with another feature of the present invention, the bypass steam is uniformly distributed over a circumference in the bypass inlet region by the torus-like annular space.
In accordance with another feature of the present invention, the torus-like annular space is formed by the U-shaped profile element defining a boundary of the outside diameter and at least a partial axial boundary on both sides.
In accordance with another feature of the present invention, the torus-like annular space is formed by an appropriate configuration of the inner casing for defining a boundary of the inside diameter and at least a partial axial boundary on both sides.
In accordance with another feature of the present invention, the U-shaped profile element is configured so as to be self-sealing against a partly expanded steam in the blade passage in the bypass inlet region, when a bypass-steam having a comparatively higher bypass-steam pressure in the torus-like annular space is utilized.
In accordance with another feature of the present invention, the inner casing, in the bypass inlet region, includes apertures. The apertures are disposed as at least one connection between the torus-like annular space and the blade passage. The apertures are further disposed and configured such that a homogeneous mixing of the bypass steam bypass-steam having a comparatively higher bypass-steam pressure from the torus-like annular space and the partly expanded steam in the blade passage is achieved in the bypass inlet region.
With the foregoing and other objects in view, there is provided, in accordance with the present invention, a method of feeding bypass steam into a steam turbine, which includes the steps of controlling a live steam through at least one valve arrangement, feeding the live steam via a quick-closing valve, and partially feeding the live steam to a turbine inlet region via at least one live-steam control valve. The method further includes the step of partially feeding the live steam as bypass steam to a bypass inlet region in a high-pressure region of the steam turbine via at least one bypass control valve.
In accordance with another feature of the present invention, the bypass steam is fed into a high-pressure region via a bypass line and via a bypass feed, although the bypass steam is not fed in until after a first turbine moving-blade row, which follows downstream of the steam-turbine inlet region.
In accordance with another feature of the present invention, the bypass steam is uniformly distributed over a circumference of the steam turbine by a torus-like annular space in the bypass inlet region.
In accordance with another feature of the present invention, the bypass steam is fed from a torus-like annular space into a blade passage via a plurality of apertures.
In accordance with another feature of the present invention, the method further includes the step of controlling a mixing of the bypass steam and a partly expanded steam in a blade passage by a configuration of the apertures.
In accordance with another feature of the present invention, the method further includes the step of controlling a mixing of the bypass steam and a partly expanded steam in a blade passage by a quantity and a position of the apertures.
Accordingly, the steam turbine has a quick-closing valve to which both of the at least one live-steam control valve and at least one bypass control valve are assigned. This achieves the effect that a large quantity of live steam is fed via the quick-closing valve. In this way, the live-steam pressure in the pressure generator is kept at the original pressure value, so that the steam generator advantageously need not be configured for a higher pressure.
A separate bypass quick-closing valve, which otherwise has to be connected upstream of each bypass control valve for safety reasons, is also eliminated in the configuration, according to the present invention. The quick-closing valve ensures the safety function for both of the control valves: the live-steam control valve and the bypass control valve.
Accordingly, a considerable increase in the output of the steam turbine, for example 50%, is achieved with comparatively few technical adaptations. This includes adaptations, such as the size of the quick-closing valve: technically complicated adaptations solely due to pressure, for example, thicker walls of pipes or casings, changes of materials to higher-grade steels or design adaptation of the steam turbine, are not necessary.
A further advantage is due to the improved control behavior of the steam turbine. Owing to the type of construction, live-steam control valves and bypass control valves are not completely steam-tight. In the steam turbine according to the present invention, live steam is always admitted to the bypass control valve during operation, since the common quick-closing valve is open. On account of the leakage of the bypass control valve due to the type of construction, a slight bypass steam constantly flows through the bypass line. Conventional constant draining of the bypass line is thus avoided. In addition, the bypass line is, thus, permanently heated. This has the advantage that the conventional heating phase for the bypass line is eliminated. Accordingly, the bypass line can be put into operation immediately on demand, that is, for example, directly after ignition of the supplementary firing of the heat recovery boiler and the higher steam production caused by it. The steam turbine, thus, has an advantageously reduced control time during a short-time demand for output.
An advantageous configuration of a steam turbine is achieved if the at least one bypass control valve, the quick-closing valve and the at least one live-steam control valve are disposed in a common valve casing. In this configuration, an optimally compact and thus space-saving steam turbine configuration is achieved.
In a preferred configuration of the steam turbine, according to the present invention, the at least one bypass feed is disposed in the high-pressure region of the steam turbine: for example, from below, as viewed in the direction of the gravitational force, such that dismantling of the bypass feed is avoided during dismantling of the top part of the outer casing of the steam turbine.
The top half, as viewed in the direction of the gravitational force, of the steam turbine according to the present invention is, therefore, freely accessible, for example for maintenance work. This is especially advantageous, when performing the maintenance work, because the top outer casing can be dismantled as simply as possible.
In a steam turbine configured according to the present invention, a bypass inlet region, at which the bypass feed feeds bypass steam into the high-pressure region of the steam turbine, is freely selectable in the axial direction between two adjacent blade rows of the turbine. In this way, the desired absorption capacity of the steam turbine can be realized in a simple manner.
An advantageously uniform distribution of the bypass steam over the circumference of the steam turbine in the bypass inlet region is achieved by a torus-like annular space.
The torus-like annular space has, on the one hand, a U-shaped profile element as a boundary of the outside diameter of the torus-like annular space. The legs of the U-shaped profile element, at least partly, form its axial boundary on both sides. On the other hand, the inner casing of the steam turbine, by appropriate configuration, forms the boundary of the inside diameter of the torus-like annular space. Likewise, the axial boundary on both sides is at least partly formed by appropriate configuration of the inner casing. In this way, the torus-like annular space is advantageously formed with relatively fewer components having simple configuration.
In addition, the U-shaped profile element, with the comparatively higher bypass-steam pressure in the torus-like annular space being utilized, is configured so as to be self-sealing against the already partly expanded steam in a blade passage in the bypass inlet region of the steam turbine. Thus, a complicated sealing construction is avoided.
A further advantage of the steam turbine configured according to the present invention is: the inner casing, in the bypass inlet region, has apertures as connections between the torus-like annular space and the blade passage. These apertures are disposed and configured in such a way that a homogeneous mixing of the bypass steam from the torus-like annular space and the partly expanded steam in the blade passage is achieved in the bypass inlet region of the steam turbine. In this way, the desired homogeneous mixing of bypass steam and partly expanded steam is achieved with especially simple technical measures.
Further, according to the method of feeding bypass steam into a steam turbine the present invention, first the live steam is fed from the steam turbine via a quick-closing valve, and, is then partly fed via at least one live-steam control valve, to the turbine inlet region. In addition, the live steam can be fed partly as xe2x80x9cbypass steamxe2x80x9d to a bypass inlet region in the high-pressure region of the steam turbine, via at least one bypass control valve.
The steam flow is advantageously directed to the steam turbine in a simple manner, because the live steam splits up into live steam and bypass steam, downstream of a quick-closing valve. Accordingly, an additional safety fitting, namely a separate bypass quick-closing valve, is advantageously omitted.
In addition, the steam pipelines are advantageously run in a simplified manner. Accordingly, it is possible to plan a more compact configuration of the steam turbine.
The overall bypass efficiency is improved, since a component causing the flow resistance, namely the bypass quick-closing valve, is thereby omitted. In addition, the requisite length of the steam pipelines is advantageously shortened.
In a further advantageous of the method according to the present invention, the bypass steam is fed into the high-pressure region of the steam turbine, via a bypass line and via a bypass feed, although the bypass steam is not fed in until after the first turbine moving-blade row, which follows downstream of the steam-turbine inlet region.
Accordingly, only one bypass line and one bypass feed are provided, thus, ensuring a simple and short pipeline run. This, moreover, keeps the pressure losses between bypass control valve and steam turbine low.
Other features which are considered as characteristic for the present invention are set forth in the appended claims.
Although the present invention is illustrated and described herein as embodied in a steam turbine and a method of feeding bypass steam, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the present invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the present invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.